Crawling The Deep Web
A vast amount of Web pages lie in the deep or invisible Web. These pages are typically only accessible by submitting queries to a database, and regular crawlers are unable to find these pages if there are no links that point to them. Google's Sitemaps protocol and mod oai are intended to allow discovery of these deep-Web resources.
Deep Web crawling also multiplies the number of Web links to be crawled. Some crawlers only take some of the -shaped URLs. In some cases, such as the Googlebot, Web crawling is done on all text contained inside the hypertext content, tags, or text.
Strategic approaches may be taken to target deep-Web content. With a technique called screen scraping, specialized software may be customized to automatically and repeatedly query a given Web form with the intention of aggregating the resulting data. Such software can be used to span multiple Web forms across multiple Websites. Data extracted from the results of one Web form submission can be taken and applied as input to another Web form thus establishing continuity across the Deep Web in a way not possible with traditional web crawlers.
Read more about this topic: Web Crawler
Famous quotes containing the words crawling, deep and/or web:
“The wind and the rain, gives this place a gleam that just isn’t natural. And the ground, alive with crawling things, crawling death.”
—Edward D. Wood, Jr. (1922–1978)
“While they stand at home at the door he is dead already,
The only son is dead.
But the mother needs to be better,
She with thin form presently drest in black,
By day her meals untouch’d, then at night fitfully sleeping, often waking,
In the midnight waking, weeping, longing with one deep longing,
O that she might withdraw unnoticed, silent from life escape and
withdraw,
To follow, to seek, to be with her dear dead son.”
—Walt Whitman (1819–1892)
“But pale despair and cold tranquillity,
Nature’s vast frame, the web of human things,
Birth and the grave, that are not as they were.”
—Percy Bysshe Shelley (1792–1822)